Coagulation of neoprene latex



Patented Dec. 14, 1948 COAGULATION F NEOPRENE LATEX David G. Slovin, Providence, R. 1., assignor to United States Rubber Company, New York, N. Y., a corporation of New Jersey No Drawing. Application December 28, 1946, Seriai'No. 719,131

3 Claims. 1

This invention relates to the production of articles from neoprene latex and particularly to coagulants for neoprene or polychloroprene latex, as well as the coagulation of neoprene latex containing zinc oxide.

The term neoprene latex as used herein is employed in its usually accepted sense, i. e. the aqueous emulsion polymerizate of chloroprene which is 2-chloro-butadiene-1,3. Neoprene latex is used in the manufacture of rubber-like articles which may be produced by dipping, spreading, extruding the latex or otherwise shaping, depositing, or casting it in the desired form. These operations are well known in the art of producing articles from natural or synthetic aqueous dispersions of rubber or rubber-like materials: and such articles include shoes, caps, gloves, sheeting, thread, etc. After the neoprene latex is deposited in the desired shape and of the desired thickness on a dipping form, or is otherwise cast in the desired shape, the usual procedure is to coagulate the film or deposit with hydrochloric acid. Neoprene articles made by coagulating the latex with hydrochloric acid, however, have certain disadvantages. For example, neoprene latex coagulated with hydrochloric acid after extrusion, as into a coagulating bath in the production of neoprene latex thread, unless treated with a neutralizing agent after coagulation, has a corrosive effect on coverings applied thereto, for example yarns, and the color of the covering is often deleteriously affected. The hydrochloric acid forms hygroscopic and corrosive salts in and on the neoprene articles, which is a commercial disadvantage, especially with textile machinery where the thread is being covered with yarn or being woven into a fabric. Neoprene articles coagulated with hydrochloric acid alone also have relatively inferior aging characteristics as measured by the conventional accelerated oxygen bomb aging test.

Neoprene latex may also be coagulated by treatment with hydroxyacetic acid, which avoids the difilculties with hydrochloric acid as discussed above. However, zinc oxide, which is necessarily present in the neoprene latex compound. dissolves in the hydroxyacetic acid, forming zinc hydroxyacetate which is soluble in hydroxyacetic acid to the extent of only about two parts in 100 parts by weight of 50 per cent acid. The excess salt crystallizes out of the coagulant and forms a coating on the neoprene articles and on the equipment used in the production thereof. ,Es'-- pecially when extruding neoprene latex containing zinc oxide into a bath of hydroxyacetic acid 2 as a coagulant, the formation of the salts is deleterious to the equipment, necessitating frequent shutdowns for cleaning, and to the coagulated thread, causing difficulties in spooling.

According to the present invention, a small amount of hydrochloric acid is added to the hydroxyacetic acid, which overcomes the difilculties referred to when using hydrochloric acid alone or hydroxyacetic acid alone. When extruded neoprene latex containing zinc oxide is coagulated in a bath of hydroxyacetic acid containing a small amount of hydrochloric acid, the salts do not appreciably crystallize out, the equipment remains clean, the thread may be successfully covered without corrosion to the covering yarn, and the rubber-like material is not appreciably hygroscopic. The color of the yarn which is used to cover the thread is not attached or altered, and the thread is eminently satisfactory for commercial purposes. The finished article, such as thread, may be used immediately after drying or vulcanization without resort to additional treatments, such as the neutralization referred to above. Although my invention is not predicated upon any particular theory, I believe that the presence of small amounts of hydrochloric acid in hydroxyacetic acid coagulant solution increases the solubility of zinc hydroxyacetate in the coagulant from a normal degree of solubility of 2 parts to an improved solubility of not less than 5 parts per 100 by weight of the coagulant solution; and since the equilibrium amount of zinc hydroxyacetate is about 4 parts in 100 of hydroxyacetic acid under the conditions normally prevailing, the crystallization of deleterious salts is prevented. It thus appears that the solubility of the zinc hydroxyacetate salts in hydroxyacetic acid is increased to a point at which the salt does not crystallize out, by the feature of the invention which includes the addition of a small amount of hydrochloric acid to the coagulant solution. The neoprene article may be made by dipping, spreading, extruding, or other vention: a neoprene latex composition was compounded as follows, the parts being by weight (dry):

Ingredients aa gz Neoprene latex (50% solids) 100 Zinc ox e Clay.- 10 Soap 2 Wetting and dispersing agents l Antioxidant 2 Water to 50% solids The ingredients were added to the neoprene latex in conventional manner by adding as aqueous solutions or suspensions. The prepared latex compound was then flowed through nozzles in the conventional manner for making latex thread, into a 50 percent aqueous solution of hydroxyacetic acid containing 0.75 percent hydrochloric acid. The thread was then dried and vulcanized continuously at a temperature of 350 C., for a period of 2 minutes, after which it was in finished form requiring no further processing or neutralizing treatment. Portions of the thread were then covered in conventional manner with cotton yarn. Both the covered and uncovered thread aged well, the yarn was not corroded, and salts did not crystallize on the yarn or on the apparatus, nor was the thread hydroscopic. The threads clearly show the advantages of coagulation by hydroxyacetic acid with small amounts of hydrochloric acid added thereto; the covering of the threads was not discolored or corroded.

In view of the many changes and modifications that may be made without departing from the principles underlying the invention, reference should be made to the appended claims for an understanding of the scope of protection afforded the invention.

Having thus described my invention, what I claim and desire to protect by Letters Patent is:

1. The method of coagulating polychloroprene latex containing zinc oxide which comprises treating the polychloroprene with an aqueous solution comprising hydroxyacetic acid having av concentration between 15 and percent and hydrochloric acid having a concentration between 0.5 and 5 percent, the concentrations being based on the weight of the aqueous solution.

2. The method of coagulating extruded polychloroprene latex containing zinc oxide which comprises treating the extruded polychloroprene latex with an aqueous solution comprising hydroxyacetic acid having a concentration between 15 and 70 percent and hydrochloric acid having a concentration between .5 and 5 percent, the concentrations being based on the weight of the aqueous solution.

3. In the method of making an article from shaped polychloroprene latex containing zinc oxide, the step which comprises treating the shaped polychloroprene latex with an aqueous solution comprising hydroxyacetic acid having a concentration between 15 and 70 percent and a hydrochloric acid having a concentration between 0.5 and '5 percent, the concentrations being based on the weight of the aqueous solution.

DAVID G. SLOVIN.

REFERENCES CITED UNITED STATES PATENTS Name Date Kirby Apr. 13, 1937 OTHER REFERENCES Number Palomaa, C. A. 8, page 1772 (.1914), (abstract from Ann. Acad. Sc. Fennicae 4, 71-104). 

